Due to a recent demand for resource saving, LED lamps, which have a longer life and require less electricity to work, have been commercialized, and additional research studies are in progress.
Such a bulb-type LED lamp generally has a single mounting substrate and a plurality of LED chips mounted on the mounting substrate, and a circuit unit for lighting the LED chips is housed in an inner space of a housing provided between the back side of the mounting substrate and a base.
When used as a substitute for an incandescent light bulb, the bulb-type LED lamp is required to present the closest possible light distribution characteristics to the incandescent light bulb. Specifically, assume the case where the bulb-type LED lamp is placed to face downward. In this case, the bulb-type LED lamp is required to emit light in a broad range, namely, obliquely backward and laterally, in addition to downward.
However, the light distributed by the bulb-type LED lamp exhibits Lambertian characteristics to be directed strongly along a specific direction, and, by its nature, illuminates a limited area right under the lamp and its neighborhood. To address the problem, a bulb-type LED lamp which includes a globe having an opening near the mounting substrate and covering the entire mounting substrate has been conceived (Patent Literature 1). This LED lamp is designed to yield the broadest possible light distribution range, by making the globe from a translucent milk-white material or the like so that the light emitted from the LEDs (i.e. LED chips) is diffused while it passes through the globe.
According to the above technology, however, the light emitted from the LEDs mostly passes through some sections of the globe ahead of the LEDs due to the Lambertian direction characteristics, and the diffusion can only produce a limited effect.
In view of the above problems, the applicant of the present application previously filed an application for an improved LED lamp in which a light diffusing member is provided between the front side of the mounting substrate and the globe.
According to the invention previously filed, a portion of the light emitted from the LEDs is diffused (i.e. scattered) by the light diffusing member positioned ahead of the LEDs and radiated after passing through broader sections of the inner surface of the globe than before. As a result, the light distribution characteristics is improved.
[Citation List]
[Patent Literature]
[Patent Literature 1] Japanese Patent Application Publication No. 2009-037995.
[Patent Literature 2] Japanese Patent Application Publication No. 2010-086713.